When you are wearing a turtleneck sweater and you fart, the fart gasses will travel up your pants, up your sweater, and exit through the turtle-neck opening at the top of your shirt. The turtle neck acts similar to a funnel on a steamboat (aka steamship, steamer).

After finishing a two-pound burrito and leaving the restaurant in his turtleneck, Javier was farting so much he resembled a paddle steamboat traveling down the Mississippi.